This invention generally relates to a drop-on-demand ink jet printer having a droplet separator that includes a mechanism for assisting the selective generation of micro droplets of ink.
Drop-on-demand ink jet printers selectively eject droplets of ink toward a printing media to create an image. Such printers typically include a print head having an array of nozzles, each of which is supplied with ink. Each of the nozzles communicates with a chamber that can be pressurized in response to an electrical impulse to induce the generation of an ink droplet from the outlet of the nozzle. Such printers, commercial and theoretically-known, use piezoelectric transducers, thermally-actuated paddles, change in liquid surface tensions, etc. to create the momentary forces necessary to generate an ink droplet. Each of the known technologies has advantages and disadvantages.
The present invention proposes a microfluidic system for providing momentary forces necessary to generate an ink droplet, and to provide an attractive alternative to known technologies. Microfluidic systems are very important in several applications. For example, U.S. Pat. No. 5,445,008 discloses these systems in biomedical research such as DNA or peptide sequencing. U.S. Pat. No. 4,237,224 discloses such systems used in clinical diagnostics such as blood or plasma analysis. U.S. Pat. No. 5,252,743 discloses such systems used in combinatorial chemical synthesis for drug discovery. U.S. Pat. No. 6,055,002 also discloses such systems for use in ink jet printing technology.
According to a preferred embodiment of the present invention, a drop on demand ink jet printing system includes an ink flow chamber having a nozzle opening in a wall of the flow chamber through which ink droplets are ejected when ink in the flow chamber is at or above a predetermined positive pressure. An inlet channel opens into the flow chamber to supply ink to the flow chamber at or above the predetermined pressure. An outlet channel communicates the flow chamber with a low pressure ink reservoir such that ink is normally transported from the flow chamber at a flow velocity sufficient to maintain ink in the flow chamber at a pressure less than the predetermined positive pressure. A valve selectively restricts the flow of ink through the outlet channel sufficiently to cause an increase in ink pressure in the flow chamber to at least the predetermined positive pressure, whereby an ink droplet is ejected through the nozzle opening.
According to another preferred embodiment of the present invention, a microfluidic system includes a fluid flow chamber having a nozzle opening in a wall of the flow chamber through which fluid droplets are ejected when fluid in the flow chamber is at or above a predetermined positive pressure. An inlet channel opens into the flow chamber to supply thermally-responsive fluid to the flow chamber at or above the predetermined pressure. A microfluidic outlet channel communicates the flow chamber with a low pressure fluid reservoir such that thermally-responsive fluid is normally transported from the flow chamber at a flow velocity sufficient to maintain fluid in the flow chamber at a pressure less than the predetermined positive pressure. A valve selectively restricts the flow of the thermally-responsive fluid through the microfluidic outlet channel sufficiently to cause an increase in fluid pressure in the flow chamber to at least the predetermined positive pressure, the valve including a heater in contact with at least a portion of the associated microfluidic outlet channel, whereby the viscosity of the thermally-responsive fluid can selectively be increased by heat from the beater to restrict the flow of the thermally-responsive fluid from the flow chamber such that an fluid droplet is ejected through the nozzle opening.
According to still another preferred embodiment of the present invention, a drop on demand microfluidic ink jet printing system includes an ink flow chamber having a nozzle opening in a wall of the flow chamber through which ink droplets are ejected when ink in the flow chamber is at or above a predetermined positive pressure. An inlet channel opens into the flow chamber to supply thermally-responsive ink to the flow chamber at or above the predetermined pressure. A microfluidic outlet channel communicates the flow chamber with a low pressure ink reservoir such that thermally-responsive ink is normally transported from the flow chamber at a flow velocity sufficient to maintain ink in the flow chamber at a pressure less than the predetermined positive pressure. A valve selectively restricts the flow of the thermally-responsive ink through the microfluidic outlet channel sufficiently to cause an increase in ink pressure in the flow chamber to at least the predetermined positive pressure, the valve including a heater in contact with at least a portion of the associated microfluidic outlet channel, whereby the viscosity of the thermally-responsive ink can selectively be increased by heat from the heater to restrict the flow of the thermally-responsive ink from the flow chamber such that an ink droplet is ejected through the nozzle opening.